US2357452A - Aluminum alloys - Google Patents

Description

-. the copending application.

Patented Sept. 5, 1944 ALUMINUM ALLOYS Walter Bonsack, South Euclid, Ohio, assignor to The National Smelting Company, Cleveland, Ohio, a corporation of-Ohio No Drawing. Application December 1, 1941,

Serial No. 421,244 f 4 Claims. (Cl. 75-141) This invention relates to alloys, and more part ticularly to machinable aluminum base alloys -having low thermal expansion and-relatively.

high wear resistance. Aluminum alloys having relatively low thermal expansion, together with relatively high strength and hardness, and retaining these properties after exposure to prolonged high temperatures, are especially desirablefor the manufacture of castings, such as pistons or other parts, for use in internal combustion engines and the like.

Aluminum-silicon alloys containing suitable amounts of manganese and magnesium have been used in the production of such pistons; and in these alloys as the proportion of silicon is increased, the thermal expansion of the alloy is decreased, and thehardness and wear resistance of the alloy are increased. Their wear resistance, however, has not been as great as usually desired and'the expansion has not been lpw enough. This is because it has usually been necessary to have the percentage of silicon less than about 15%, as higher amounts of silicon have decreased the machinability and fatigue resistance of the alloy to a substantial degree.

In my copending application Serial No. 388,491,

filed April 14, 1941, there is disclosed an'alloy containing silicon, magnesium, copper, iron, zinc,

tin, and at least one or more elements such as manganese, nickel, chromium, cobalt, titanium, columbium, molybdenum, tungsten, vanadium, zirconium, boron, tantalum and cerium. It has now been found that a very desirable alloy may be obtained without utilizing tin as specified in The tin may be replaced by the zinc or partly by the Zinc and other hardeners, as will be more fully explained hereafter. a

The alloys of the present invention contain 18% to 35% silicon, about .l% to 1% magnesium, about .3% to 4% copper, about .4% or amount from about 20% to'.30% of the alloy. Silicon increases the hardness and wear resistance,of the alloy and decreases its thermal expansion. Without suitable quantities of the other above mentioned constituents, however, it has a tendency to crystallize into relatively large crystals and tQ-decrease the machinability of the alloy.

Iron tends to harden the alloy, decrease its thermal expansion, increase its machinability, and aids in maintaining the properties of the alloy at relatively high temperatures. It is preferably present within the amounts of about .7 to 1.5%, although an alloy having very desirable properties may be obtained with 2% or so iron present, and with as little as about .4% or .5%. Iron, however, like silicon, has the property of tending to crystallize into relatively large crystals in the absence of hardening metals of the/ groups set out above.

The members of the above groups each tend to harden the alloy, decrease its thermal expansion and increase its machinability. They are also beneficial in that they tend to maintain the desirable properties at relatively high temperatures, such as those encountered in internal combustion engines and the like.

Metals of the above group of hardening metals consistingof manganese, nickel, cobalt and chromium are usually most desirable in the alloy for the reason that they are more easily alloyed with the aluminum and most desirable properties are obtained whenat least one of these metals is present. These four elements function in aluminum alloys as hardeners and have no appreciable function as grain refiners.

.5% to 2% iron, about .3% to 4% zinc, and at least one' of the hardening metals selected from the group consisting of manganese, nickel, chromium, cobalt, titanium, columbiuml molybtantalum and cerium in a total amount of 5% or less. Preferably, one or more of the elements manganese, nickel, chromiumv and cobalt are present in the alloy in a substantial amount (.3% or more) with a total not substantially in excess Ihe hardening and grainrefining metals of the group consisting of columbium, molybdenum, tungsten, vanadium, zirconium, cerium, titanium, tantalum and boron are generally recognized as being both hardeners and grain refiners in aluminum alloys. If grain refining is not particularly desirable, as when the whole casting denum, tungsten, vanadium, zirconium, boron, A

of 3%. Also, one or more of the remaining metals is preferably present but not substantially in. excess of 2%. The alloy should preferably have the hardening metals present in amount of .3%

or more. 1

Silicon, which aside from aluminum is the predominant alloying ingredient, may be present in the alloywithin the limits of 18% to 355%; but, siiioon is preferably present in an is chilled substantiallysimultaneously, it may not be necessary to use any 01 these elements. However, it is preferable to have at least one present even though one-or more of the above group consisting of manganesepcobalt, chromium and nickel be also present. I

The desirable proportions of the elements in the above mentioned groups which are effective to obtain my improved results"ar e different; Thus, desirable properties may be obtained with any of the following elements: manganese in amount of about .2% to 1%; nickel in amount of about'.2% to 1.5%; chromium in amount of about .l% to .5%; cobalt in amount of about .1% to .5%; columbiurn in amount of about .01% to 25%; molybdenum in amount of about .l% to 5%; tungsten in amount of about .l% to ,5%;

vanadium in amount of about .1% to .5%; zirconium in amount of about .01% to .25%; cerium in amount of about .01% to 25%.; titanium in amount of about .05% to .3%; tantalum in amount of about .1 to .3%; and boron in amount of about .005% to .1%. l

Since each of these hardening metals vmay tend to crystallizein somewhat different shapes, finer crystals and more desirable properties may be obtained in alloys having more than one of these metals present, each in relatively smaller amounts than in alloys having thesame total effective amount" of a lesser number of these metals.

The members of the above mentioned groups have the desirable property of tending to inhibit the growth of the large iron and silicon crystals, especially when two or more of the members are present. two or more of these elements present, even though there be present a relatively large amount of iron. However, with a relatively large iron content, a somewhat smaller total quantity of these elements may be used to obtain substantial ly the same properties in the alloy as when a smaller amount of iron is present.

The total quantity of the hardening and grain refining metals in the above groups should be less than 5% and they Should be present in an amount of about .8% or more, and preferably 1% or more of the alloy. In the preferred alloys having manganese, chromium, nickel, and zinc,

with one of the grain refining and hardenig' group, such as titanium, present, the preferred amount of manganese is about .'7%; the preferred amount of nickel is around l%; the preferred amount of chromium is around .2%; and the preferred amount of titanium is about .15% to 2%.

Magnesium, as well as improving the hardness and tensile strength of aluminum-silicon,

alloys, increases the elastic properties of the alloy, and also improves the machinability, and is preferably present in amounts of about .3% to-about .8%, although as much as 1%, or even somewhat more, may be used, and an appreciable effect is obtained with as little as about .1%.

Copper is animportant ingredient of my improved alloy and is preferably present in amounts of about 1% to 2%. strength, fatigue strength and hardness of the alloy, as well as improves its machinability. The

' amountof copper preferred depends to some extent on the zinc content and the particular application to which the alloy is to be put. When the zinc is low it is often desirable to have more copper present. In case the alloy is to be used as a bearing, it is desirable that both copper and zinc be present in the larger amounts. Zinc has the effect of improving the tensile strength and hardness of aluminlm alloys and also improves the machinability and increases hardness. It

Consequently, it is desirable to have.

Copper increases the tensile The following examples illustrate the present invention:

Example 1 An aluminum base alloy containing 21% of silicon, about 2% copper; about .6% of manganese, about .4% magnesium, about .8% iron, about .4% nickel, about .5% of zinc, was chill cast into test bars, which were quenched from the mold and heat treated twelve hours at 355 F. The hardness of the bars thus obtained averaged about 142 Brinell. Their tensile strength was about 30,500 lbs. per square inch.

The castings made from the alloy may be readily machined, have relatively great wear resistance, relatively low thermal expansion and excellent fatigue strength.

Example 2 When the zinc content of the alloy of Example.

' and heat treated twelve hours at 355 F., was becan be used advantageously in the present alloy I in amounts from about .3% to 4%, and it is preferable to have the zinc present'in amounts from about .'7% to about 2.5%.

Zinc even in the higher ranges has the property of remaining in solid solution and does not separate from a cast;

sirable for parts which are subjected to hightemperatures.

tween 28,800. lbs. per square inch and 31,700 lbs. per square inch. The Brinell hardness was between and 140. Castings made from the alloy were readily machined and had very desirable wear resisting properties.

The alloys of the present invention are particularly desirable for the production of castings, and the castings are susceptible to the usual heat treatments and have their tensile strength and hardness substantially improved thereby.

Furthermore, it is to be understood that various modifications of the alloys disclosed herein can be made without departing from my invention as defined in the appended claims.

What I claim is:

1. An aluminum base alloy having a relatively low coefficient of thermal expansion and relativelygreat wear resistance, containing 18% to 35% silicon, about .1% to 1% magnesium,-about .3% to 4% copper, about .4% to 2% iron, about .3% to 4% zinc, and one or more of the hardening and grain refining metals, with the balance substantiallyall' aluminum and minor impurities.

2. An aluminum base alloy'having a relatively.

low coefficient of thermal expansion and relatively great wear resistance, containing 20% to 530% silicon, about .1% to 1% magnesium, about ing and grain refining metals, with the balance' substantially all aluminum and minor impurities.

3. An aluminum base alloy having a relatively low coeflicient of thermal expansion and rela-. tively great wear resistance, containing 18% to 35% silicon, about .3% to .8% magnesium, about 1% to 2% copper, about .'7% to 1.5% iron, about .'7% to 2.5% zinc, and one or more of the hardening and grain refining metals, with the balance substantially all aluminum and minor impurities.

4. An aluminum base alloy having a relatively low coefficient of thermal expansion and relatively great wear resistance, containing 18% to 35% silicon, about .1% to 1% magnesium, about .3% to 4% copper, about .4% to'2% iron, about -.3% to 4% zinc, and about .2% to 1% manganese, with the balance substantially all aluminum and minor impurities. Y

. WALTER BONSACK.